Improved black writing pencil leads



. photographic printing.

Patented Oct. 8, 1935 FA'E'ENT OFFICE August Schwarz and Karl Kreutzer,Nuremberg,

Germany, berg, Germany, a firm assignor to J. S. Staedtler, Nurem- NoDrawing. Application March 14, 1933, Serial 2 Claims.

This invention relates to the production of leads for writing anddrawing pencils to be used for preparing documents and drawings whichare intended to be directly reproduced by means of The pencil leads,composed of graphite and clay, are saturated with fatty material(tallow, stearin, wax and the like), for the purpose of improving theirwriting capability. This fatty material is mix-ed with a fatsolublecolouring material or dyestufi in order to raise the light opacity ofthe lead that is making the writing or printing dense to light.

This invention consists on the one hand in using a colouring material ordyestufi which is soluble in the agent for fixing the marks and on theother hand in preliminarily impregnating the leads with the dyestufi orcoloring material.

The first part of the invention is carried out as follows;

A colouring material or dyestuii is added to the fatty mass used formaking the lead, which is soluble in an ordinary agent for fixing themarks, e. g. a solution of shellac in alcohol, for the purpose ofproducing a black lead mark on tracing paper which is light opaque likean India ink mark. This effect is obtained by the dye-stun forming oneconstituent of the lead mark being made to flow under the action of thefixing agent and to distribute itself in the mark so as to make thelatter uniformly black, that is dense to light.

The so-called Sudan dyestuffs of the I. G. Farbenindustrie A. 6%., moreparticularly Sudan yellow, are adapted as colouring materials ordyestuffs for use in accordance with this invention.

The second part of the invention is carried out as follows:

A fat-soluble dyestuff, e. g. Sudan yellow, is first of all dissolved ina solvent which is thinly liquid at ordinary temperature, e. g. alcohol,benzine, and so forth. The leads are soaked in this dye solution. Thesolvent is then removed by dry- In Germany April 11, 1932 ing, whereuponthe dyestuff previously present in the solvent now remains behind in thelead. The leads preliminarily dyed in this way are then prepared bymeans of a fatty mass to which is added a similar dyestufi.Particularly, however, dyestuffs are used which are soluble in thefixing agent.

The preliminary colouring of the lead ensures that the latter takes upsubstantially more dyestuff and consequently the blackness or density 10of the marks produced with the leads with reference to light isenhanced. Moreover, the process enables fat masses to be employed havingsmaller solvent capability for dyestuffs.

The term writing in the claims is intended to also include drawing andprinting.

Having now particularly described and ascertained the nature of thisinvention and in What manner the same is to be performed, we declarethat what we claim is:

1. A method of increasing the opaqueness to light of the black Writingfrom a lead pencil, which consists in impregnating an ordinary pencillead with a fat soluble dyestui'i dissolved in a substance which isthinly liquid at ordinary temperature, said substances being selectedfrom a group consisting of alcohol and benzine whereby, upon suchwriting coming in contact with a fixing agent containing such substancesthe writing becomes substantially impenetrable to light, then drying thelead leaving the dyestufi therein.

2. A black writing pencil comprising as main constituent a lead and asubstance impregnated in said lead adapted to make the writingsubstantially impenetrable to light for photographic 35 printing; saidsubstance consisting of a fat soluble dyestuff dissoluble in a shellacsolution in alcohol used as fixing agent for the writing.

